1. Field of the Invention
The field of the invention is dental appliance manufacturing.
2. Description of the Related Art
Orthodontic aligners are appliances intended to make a series of discrete tooth position corrections aimed at aligning the teeth correctly. Aligners are equivalent to having bracket/wire braces for orthodontic treatment but they have many advantages. For example, aligners are invisible, comfortable and removable for cleaning and they allow a patient to eat anything they want. The manufacture of aligners begins with making stone models from dental impressions that come from orthodontists. The stone models of the dental impressions provide a positive model of the teeth, also known as the dental arch.
The stone models are scanned electronically to produce three dimensional computer aided design (CAD) representations to be imported by custom software. The custom software allows the operator to move individual teeth in specific and discrete movements to achieve the final dental arch of aligned teeth. The typical tooth movement is 0.1 mm per week.
Each aligner is meant to be worn for three weeks, then the patient moves on to wear the next aligner. A patient will typically wear aligners for somewhere between 18 to 36 weeks. For example, a treatment that takes 18 weeks is 6 pairs of aligners, including upper and lower dental arches.
The software allows the operator to create a stepwise sequence of teeth positions from start to finish via 6 stages, for example for an 18 week treatment plan. In the 18 week example, the software will create 6 pairs of models of dental arches. The resulting adjusted and predictive models of the dental arches are then printed as 3D models.
The 3D models are washed and then the models are allowed to dry. Once dried, a polymer is thermoformed over the top of the 3D model.
The thermoformed part is then laser marked with part identification. The laser marked, thermoformed part is then cut by one of several methods so that the aligner that goes to the customer can be separated from the carrier frame of plastic.
The aligner is then polished in a part tumbling process to remove burrs and sharp edges. The aligners are inspected and then sealed in bags to be shipped to the customer's orthodontist.
The aligners are currently thermoformed individually. For example, the Biostar® thermoformer, by Great Lakes Orthodontics, Ltd., uses positive pressure to thermoform a single aligner. The Biostar® thermoformer also does not allow full and variable control of the heater that is used to heat the polymer during the thermoforming process.
An aligner thermoformer that is capable of producing a series of aligners is shown in U.S. Pat. No. 7,261,533 (“the '533 patent”). The '533 patent is highly complex and does not allow for the production of a batch of aligners simultaneously. It also has one production speed and must be operated in a continuous mode, which does not allow the operator to make just a single aligner. While the temperature set point can be adjusted on the '533 patent, the temperature set point will apply to all aligners as they are produced in series. The '533 patent employs positive pressure to thermoform each aligner while vacuum is used to prevent bubbles from forming during the thermoforming process.
What is needed is a thermoformer for manufacturing aligners that produces a batch of aligners with the ability to control the temperature set point for each aligner forming location. The number of aligners to be produced could be increased by increasing the number of thermoforming stations.
The new thermoformer should also only use vacuum to evacuate the gas out of the region between the softened polymer and the dental model to more exactly conform the aligner to the dental model. The more accurate adaptation of aligners to the dental models will result in better performance of the aligners for patients and customers.
The new thermoformer should make parts faster and it should cost less than existing technology. It should also allow more control of the thermoforming process.